This invention relates to a magnetic sensor system for spindle orientation whereby the spindle of a machine tool or the like is stopped at a fixed position in a contactless manner. More particularly, the invention relates to a mounting structure for mounting a magnetic body of the magnetic sensor system on the spindle.
A magnetic sensor system for spindle orientation in which the spindle of a machine tool or the like is stopped at a fixed position in a contactless manner, ordinarily is adapted to extract a position feedback signal from a magnetic sensor directly connected to the spindle and to process the signal by an orientation circuit. The position feedback signal is for the purpose of detecting the position of a rotary shaft. A magnetic signal from a magnetic body attached to the spindle at a prescribed position thereon is detected and extracted by a sensing unit arranged on a mechanically stationary member.
FIGS. 6(A), (B) are diagrams showing an example of the arrangement of a position detector for detecting the position of a spindle 1. FIG. 6(A) is a side view and FIG. 6(B) is a cross-sectional view along the cross-section; of the rotating spindle 1.
In order to stop a prescribed portion of the spindle 1 at a fixed position, the position detector comprises a magnetic body 10 attached to the spindle at a rotational angle which is the same as that of the prescribed portion, and a sensing unit 11 for producing a magnetic signal delivered to an orientation circuit 12. As shown in FIG. 6(C), the magnetic body 10 has two rubber magnets 10b of triangular cross section accommodated in a case 10a, and is mounted in such a manner that the magnetizing strength thereof changes continuously from the S pole to the N pole in the direction of spindle rotation (the direction of the arrow). The sensing unit 11 is mounted on a mechanically stationary member in the neighborhood of the spindle 1 to confront the magnetic body 10 across a distance of 1 to 2 mm.
As shown in FIG. 6(C), the sensing unit 11 is composed of three saturable reactors SRA.sub.1, SRA.sub.2, SRA.sub.3 arranged side by side in a case 11a. Each saturable reactor has a core CR on which coils L.sub.1, L.sub.2 are wound to produce mutually opposing polarities, as shown in FIG. 6(D). The coils L.sub.1, L.sub.2 have a common terminal TA to which a high-frequency signal from the orientation circuit 12 is applied, as well as respective terminals TB, TC from which a magnetic signal corresponding to the position of the magnetic body 10 is produced.
FIG. 6(E) is a waveform diagram of output signals PDS, ASV obtained from the orientation circuit 12 when the magnetic body 10 and sensing unit 11 are positionally related as shown in FIG. 6(C).
ASVa, PDS, ASVb indicate output voltage waveforms obtained from the sensing unit and corresponding to the respective saturable reactors SRA.sub.1, SRA.sub.2, SRA.sub.3 of the sensing unit 11. The orientation circuit 12 is so arranged that the sensing circuit produces an output voltage of zero as the center line of the magnetic body 10a successively achieves coincidence with the center lines of the saturable reactors SRA.sub.1, SRA.sub.2, SRA.sub.3, a positive output voltage at a position near the left of each center line, and a negative output voltage at a position near the right of each center line. Therefore, ASVa, PDS and ASVb have an overall voltage waveform that crosses the zero level. The voltage signal PDS is used as a rotation deviation signal of the spindle 1. A voltage signal ASV is the sum of a voltage waveform obtained by shifting the phase of the sensing circuit output ASVa by 180.degree., and the output ASVb of the sensing circuit. The voltage signal ASV is used as a signal indicating that the prescribed portion of the spindle 1 has arrived near the fixed position.
Though the position of the spindle 1 may be detected by arranging the position detector in the foregoing manner, the output signal ASV can be outputted as the voltage waveform shown in FIG. 6(F) besides the form shown in FIG. 6(E). Details regarding the construction of a spindle position detector of this type are disclosed in Japanese patent application Laid-Open Nos. 56-54523, 56-97105, 56-97106, etc., all of which were filed and laid-open in Japan.
When cutting aluminum or a light alloy such as Duralumin with a machine for cutting workpieces, rotating the spindle of the machine at a low velocity is undesirable as it causes the cut surface of the workpiece to take on a roughened appearance and to exhibit a dull color. However, if the workpiece (such as a light alloy) is cut by rotating the machine spindle at a high velocity of, e.g., 10,000 to 20,000 rpm, the cut surface exhibits luster, even without polishing after cutting, thereby enabling an improvement in the condition of the cut surface.
Though it has been considered that large mechanical loss accompanies high-velocity rotation of a spindle and that the motor is required to have a high output for such high-velocity rotation, it is known that recent advances in spindle technology have made it possible to reduce mechanical loss and to make do with a motor having a low output, even when rotating a spindle at a high velocity.
Thus, since higher spindle velocities make it possible to obtain an excellent cut surface and lead to a more compact machine and motor, the tendency recently is to use ever higher spindle velocities.
However, with the conventional magnetic sensor system for spindle orientation, the magnetic body 10 is attached to a portion on the circumference to the spindle 1, as shown in FIGS. 6(A), (B), in order to detect the rotational position of the spindle. The result is a sound produced as the magnetic body cuts through the wind during rotation of the spindle. In addition, as the spindle 1 is rotated at ever higher velocity, the harmful influence of this effect is promoted and it also becomes necessary to improve the strength at which the magnetic body 10 is attached to the spindle 1.